Composition comprising thermoplastic starch and aliphatic polyester

ABSTRACT

The invention relates to a thermoplastic composition comprising at least one polyester (A) which is an aliphatic polyester; at least one starch (B); at least one organic plasticiser (C) for starch; and at lest one monoester compound (D) of fatty monoacid comprising at least 12 carbon atoms and glycerol. The composition is characterised in that the amount by weight of compound (D) varies between 0.05 and 1.7 parts per 100 parts of the dry weight of the different constituents (A), (B) and (C).

FIELD OF THE INVENTION

A subject of the invention is a thermoplastic composition comprisingthermoplastic starch, an aliphatic polyester and at least one monoesterof a fatty acid and of glycerol. Another subject of the invention is agranule of the composition, a manufacturing process for manufacturingsaid composition and a process for manufacturing a film by film blowingusing the composition.

TECHNICAL BACKGROUND OF THE INVENTION

Because of their numerous advantages, plastics have become inescapablein the mass manufacture of objects. Indeed, because of theirthermoplastic nature, it is possible to manufacture objects of any typefrom these polymers, at a high rate. To manufacture these objects, smallpieces of these thermoplastic polymers are used, that are melted byproviding heat and mechanical stresses in forming machines. For example,it is possible to manufacture film by introducing these pieces into ablown film extruder or a flat die extruder (cast extrusion) or else tomanufacture bottles by introducing said pieces into a blow-moldingextruder. These small pieces are in most cases in the form of granules,since said granules are very easy to handle.

These objects are generally made of non-biodegradable thermoplastics,such as polyolefins or polyamides. However, these plastics are stilltoday not recycled a great deal. Thus, this causes environmentalproblems since they are generally incinerated and this incineration cancause toxic gases to be given off. Thus, one of the importantpreoccupations today in the polymer field is to provide polymers whichare biodegradable or at least compostable.

Among the biodegradable and/or compostable polymers, mention may be madeof aliphatic polyesters, such as poly(butylene succinate) (PBS),poly(butylene succinate-co-adipate) (PBSA), poly-ε-caprolactone (pCAPA),polylactic acid (PLA) and also polyhydroxyalkanoates ofpolyhydroxybutyrate (PHB) or poly(hydroxy butyrate-co-valerate) (PHVB)type. Aliphatic polyesters generally have melting points close to thoseof polyolefins, thereby allowing, inter alia, their use in the fields offilms and packaging, the biodegradability of which is an obviousadvantage for single-use applications.

However, one of the problems of these polyesters is that they arerelatively expensive. One of the solutions envisioned for providingbiodegradable compositions which are more economical is to manufacturecompositions based on thermoplastic starch, this consisting of starchand of a plasticizer for this starch, such as glycerol. Specifically,the manufacture of these compositions is advantageous since starch isone of the biosourced polymers that is naturally the most widespread inthe environment. However, these thermoplastic starches have insufficientproperties, in particular in terms of water resistance. Furthermore,transforming starch into thermoplastic starch is not easy since itrequires the use of substantial constraints and/or temperatures duringthe thermomechanical mixing, which has a tendency to degrade thethermoplastic starch thus formed.

To counter these drawbacks, compositions based on aliphatic polyestersand plasticized starch have been developed. In these compositions, thethermoplastic starch phase is generally dispersed in the polyesterphase. These compositions have numerous advantages, for instance that ofbeing able to be composted or and/or biodegradable and of having waterresistance that is very much improved relative to thermoplastic starch.

In industrial practice, films are mainly manufactured by blown filmextrusion (or extrusion blow molding) since this technique allows themanufacture of films of large size and at a high rate. The applicant hasbeen able to note that one of the problems of these compositions basedon thermoplastic starch and aliphatic polyester is that they can, athigh rate, be tacky during the forming of the film by extrusion blowmolding. This creates problems of separation of the blown tube during orafter manufacture, once this blown tube is in the form of a spool. Thisphenomenon prevents, for example, the production of fine bags or films.This problem is specific to compositions comprising aliphatic polyestersince, contrary to other polyesters such as semi-aliphatic polyesters,they have a slow crystallization speed. The blown tube remains in themolten state and has a tendency to stick during the extrusion blowmolding process.

These problems are worsened when the amount of thermoplastic starch inthe composition and/or the amount of plasticizer in the thermoplasticstarch are high.

The applicant has succeeded in providing novel compositions which makeit possible to overcome these problems.

SUMMARY OF THE INVENTION

A subject of the invention is thus a thermoplastic compositioncomprising at least one polyester (A) which is an aliphatic polyester,at least one starch (B), at least one organic plasticizer for starch (C)and at least one compound which is a monoester (D) of a mono fatty acidcomprising at least 12 carbon atoms and of glycerol, the amount byweight of monoester (D) of which ranges from 0.05 to 1.7 parts, theseamounts by weight being expressed relative to 100 parts of the total dryweight of the constituents (A), (B) and (C).

The applicant has been able to note that, when compositions based onstarch and aliphatic polyester comprise this monoester (D) in theseparticular proportions, they have, in particular when they are in blowntube form, a much less tacky aspect than the compositions free of thiscompound (D) or else comprising these compositions in greaterproportions.

Application EP 950 690 A2 describes a composition based on thermoplasticstarch and a thermoplastic polymer which is incompatible with thisthermoplastic starch, which can be an aliphatic polyester, in which thethermoplastic starch is dispersed in a continuous phase of thermoplasticpolymer, and an interfacial agent in order to improve the waterresistance and its resistance to ageing. According to sub-variant c) ofthe family of compositions A), this interfacial agent may be of the typeof a monoester of a fatty acid comprising from 12 to 22 carbon atoms andof glycerol. In this case, this interfacial agent must be introduced inproportions of at least 10% by weight relative to the weight of thethermoplastic starch.

Application WO 2007/012142 A1 describes a composition comprisingpolycaprolactone, polycaprolactone-grafted starch, corn starch, sorbitoland glycerol and also glucose stearate. This composition has improvedproperties conferred by the presence of the grafted starch. Thisdocument does not describe a composition comprising the monoester (D)described above.

DETAILED DESCRIPTION OF THE INVENTION

A subject of the invention is a thermoplastic composition based onpolyester (A) which is aliphatic, thermoplastic starch and a monoester(D) of a mono fatty acid comprising at least 12 carbon atoms and ofglycerol.

A thermoplastic composition is a composition which, reversibly, softensunder the action of heat and hardens on cooling to ambient temperature.It has at least one glass transition temperature (Tg) below which theamorphous fraction of the composition is in the brittle vitreous state,and above which the composition may undergo reversible plasticdeformations. The glass transition temperature or at least one of theglass transition temperatures of the starch-based thermoplasticcomposition of the present invention is preferably between −150° C. and40° C. This starch-based composition may, of course, be formed viaprocesses conventionally used in plastics engineering, such asextrusion, injection, molding, blow-molding and calendering. Itsviscosity, measured at a temperature from 100° C. to 200° C., isgenerally between 10 and 10⁶ Pa·s.

The composition according to the invention also has the advantage ofbeing able to be biodegradable.

The composition according to the invention comprises at least onealiphatic polyester, which is a polyester that comprises exclusivelynon-aromatic monomers. The term “comprises monomers” is intended to meanthat the polyester can be obtained by polycondensation of thesemonomers. For example, if the polyester comprises succinic acid and1,4-butanediol, this means that it can be obtained by polycondensationof monomers comprising succinic acid and 1,4-butanediol. It is alsospecified that, when it is indicated that the polyester “comprises x %of a monomer (X)”, this means that it can be obtained from a mixture ofmonomers comprising, relative to the total weight of the monomers, x %of monomer (X).

An aliphatic polyester is a polyester that can be obtained usingnon-aromatic monomers, said monomers being chosen from polyols,polyacids and monomers bearing at least one carboxylic acid function andat least one alcohol function. These non-aromatic monomers may belinear, cycloaliphatic or branched. It is also possible to obtain thesepolyesters via enzymatic or fermentation routes, as in the case of thepolyhydroxyalkanoates.

These polyols are generally aliphatic diols, preferably saturated linearaliphatic diols. As linear aliphatic diol, mention may be made ofethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, or a mixture ofaliphatic diol units comprising at least one of these units,preferentially ethylene glycol and 1,4-butanediol or a mixture of thesediols, most preferentially 1,4-butanediol.

The polyacids are generally aliphatic diacids, preferably saturatedaliphatic diacids. By way of example, these diacids may be succinicacid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaicacid, sebacic acid or a mixture of these diacids. Preferably, thealiphatic diacid is chosen from succinic acid and adipic acid or amixture of these acids. The polyesters can also be obtained from esters,anhydrides or chlorides of these polyacids.

The monomers bearing at least one carboxylic acid function and at leastone alcohol function are generally hydroxy acids. By way of example, thehydroxy acids may be glycolic acid, lactic acid, hydroxybutyric acid,hydroxycaproic acid, hydroxyvaleric acid, 7-hydroxyheptanoic acid,8-hydroxyoctanoic acid, 9-hydroxynonanoic acid, or a mixture of thesehydroxy acids. The polyesters may also be obtained from dilactone suchas glycolide or lactide, or from lactone such as caprolactone.

Preferably, the composition comprises, as polyester (A), an aliphaticpolyester or a mixture of aliphatic polyesters.

According to the variant wherein the composition comprises, as polyester(A), an aliphatic polyester, this aliphatic polyester advantageouslycomprises 1,4-butanediol and succinic acid and/or adipic acid. Thepolyester (A) is most preferentially chosen from PBS and PBSA.

According to the variant, the composition comprises a mixture ofaliphatic polyesters; the composition advantageously comprises amixture:

-   -   of at least one polyester (A1) which is an aliphatic polyester        comprising 1,4-butanediol and succinic acid and/or adipic acid,        this polyester (A1) being most preferentially chosen from PBS        and PBSA;    -   of at least one polyester (A2) which is polylactic acid.

Preferably, the polylactic acid is a semi-crystalline polylactic acid.Polylactic acid is generally obtained by polymerization of lactide, byring opening. The lactide can be in the form of D-lactide or L-lactideor else in the form of meso-lactide. The crystallinity of the polylacticacid is mainly controlled by the amount of D-lactide and of L-lactideand to a lesser extent by the type of catalyst used. Thus, thepolymerization of a racemic mixture of L-lactide and D-lactide generallyleads to the synthesis of an amorphous polylactic acid, whereas thepolymerization of pure D-lactide or of pure L-lactide leads to thesynthesis of a semi-crystalline polylactic acid. A synthesis processusing a racemic mixture can also lead to a heterotactic PLA exhibitingcrystallinity by using stereospecific catalysts. Preferably, thepolylactic acid exhibits a crystallinity ranging from 30% to 75%, mostpreferentially from 40% to 60%. The degree of crystallinity of the PLAcan be determined by differential scanning calorimetry analysis on thebasis of the calculation of the ratio of the Cp jump values at Tg of thesemi-crystalline product that it is sought to characterize and of thesame product made completely amorphous.

According to the variant wherein the composition comprises a blend ofpolyesters (A1) and (A2), the weight percentage of (A2) relative to theweight of (A1) and (A2), expressed by dry weight, advantageously rangesfrom 2% to 70%, advantageously from 10% to 50%, preferably from 18% to30%. More preferentially, the weight percentage of (A2), relative to theweight of (A1) and (A2), expressed by dry weight, ranges from 5% to 90%,preferably from 15% to 45%.

According to another embodiment, the weight percentage of (A2) relativeto the weight of (A1) and (A2) is low, that is to say that this weightpercentage, expressed by dry weight, ranges from 2% to 20%,advantageously according to this mode from 3% to 15%, for example from4% to 10%.

According to this variant, and in particular according to thesepreferred sub-variants, it is possible to manufacture films from thiscomposition by blown film extrusion, using particularly high productionrates.

The various constituents of the composition, in particular the starch,and also the composition obtained, may comprise moisture. The weightproportions can be expressed in the present application either by “dryweight”, that is to say that the water possibly included in theconstituents or the composition is not taken into consideration for thecalculation of the weight proportion, or by “wet weight”, that is to saythat the water possibly included in the constituents or the compositionis taken into consideration for the calculation of the weightproportion.

Preferably, the polyester(s) (A) has (have) a flow index ranging from0.1 to 50 g/10 min, advantageously from 0.5 to 15 g/10 min (ISO 1133,190° C., 2.16 kg).

The composition according to the invention also comprises starch (B) andan organic plasticizer for starch (C), the two forming thermoplasticstarch.

With regard to the starch (B), it may be of any type. If it is desiredto obtain a less expensive composition, the starch preferentially usedfor the manufacture of the composition is a granular starch, preferablya native starch.

The term “granular starch” is intended to mean herein a native orphysically, chemically or enzymatically modified starch, which hasconserved, within the starch granules, a semicrystalline structuresimilar to that revealed in the starch grains naturally present in thestorage organs and tissues of higher plants, in particular in cerealgrains, legume grains, potato or cassava tubers, roots, bulbs, stalksand fruit. In the native state, starch grains generally have a degree ofcrystallinity that ranges from 15% to 45%, and which depends essentiallyon the botanical origin of the starch and on the possible treatment thatit has undergone.

Granular starch, placed under polarized light, has a characteristicblack cross, known as the Maltese cross, typical of the granular state.

According to the invention, the starch may come from any botanicalorigin, including a granular starch rich in amylose or, conversely, richin amylopectin (waxy). It may be native starch of cereals such as wheat,maize, barley, triticale, sorghum or rice, tubers such as potato orcassava, or legumes such as pea and soybean, and mixtures of suchstarches.

The starch may also be modified, chemically or physically.

The function of the organic plasticizer for starch (C) is to make thestarch thermoplastic.

It may be an organic plasticizer chosen from diols and polyols such asglycerol, polyglycerols, sorbitans, sorbitol, mannitol, and hydrogenatedglucose syrups, urea, polyethers with a molar mass below 800 g/mol, andany mixtures of these products, preferably glycerol, sorbitol or amixture of glycerol and sorbitol.

According to the invention, the composition may comprise relatively highamounts of plasticizer. Thus, advantageously, the starch/plasticizerweight ratio, expressed by dry weight, ranges from 90/10 to 40/60, forexample from 85/15 to 40/60, advantageously from 85/15 to 50/50,preferably from 80/20 to 60/40. The range from 90/10 to 40/60 can bebroken down into two sub-ranges: a sub-range from 90/10 to 85/15 (85/15limit excluded) and a sub-range from 85/15 to 40/60. According toanother preferred embodiment, the starch (B)/organic plasticizer (C)weight ratio, expressed by dry weight, ranges from 90/10 to 80/20, oreven from 90/10 to 85/15 (85/15 limit excluded). According to this mode,the weight percentage of (A2) relative to the weight of (A1) and (A2) ispreferably low. The compositions of this preferred mode make it possibleto be subsequently converted, for example in the form of a film, withoutany fumes being given off during the conversion. Moreover, the filmsobtained exhibit excellent mechanical properties, in particular when theamount of (A2) is low.

Even when the amounts of plasticizer are high, the composition accordingto the invention can be converted into the form of a blown tube, withoutsaid blown tube sticking to itself, this being even when the blown tubeis produced at a high rate. The composition then exhibits a greaterflexibility.

According to the invention, the composition may comprise very variableamounts of thermoplastic starch. Thus, the total amount by weight ofpolyester (A) may be included in the range of from 35 to 75 parts, theseamounts by weight being expressed relative to 100 parts of the total dryweight of the constituents (A), (B) and (C). It may comprise a totalamount by weight of polyester (A) ranging from 40 to 70 parts,advantageously in the range of from 40 to 60 parts, preferably in therange of from 48 to 58 parts.

The composition according to the invention can be characterized by amorphology which is in the form of co-continuous domains ofthermoplastic starch and of polyester. The morphology of the compositioncan be observed by scanning electron microscopy.

Even when the amounts of thermoplastic starch are high, the compositionaccording to the invention may be made into the form of films, withoutsaid films being tacky. In certain proportions such as those definedabove, the morphology of the composition exhibits co-continuous domainsof polyester and of thermoplastic starch. These compositions exhibitimproved biodegradability compared with compositions in which thethermoplastic starch is dispersed in a continuous phase of polyester.

According to another preferred mode, the composition comprises a totalamount by weight of polyester (A) included in the range of from 60 to 75parts, preferentially from 62 to 72 parts, these amounts by weight beingexpressed relative to 100 parts of the total dry weight of theconstituents (A), (B) and (C). Generally, this composition ischaracterized by a morphology which is in the form of thermoplasticstarch domains dispersed in a polyester matrix. According to this mode,the films obtained from these compositions exhibit better tear strengthproperties.

Even when the amounts of thermoplastic starch are high, the compositionaccording to the invention can be converted into the form of films,without said films sticking to themselves, this being possible even whenthe production rate is high. In certain proportions such as thosedefined above, the morphology of the composition exhibits co-continuousdomains of polyester and of thermoplastic starch. These compositionsexhibit improved biodegradability compared with compositions in whichthe thermoplastic starch is dispersed in a continuous phase ofpolyester.

According to the invention, the composition also comprises a compoundwhich is a monoester (D) of a mono fatty acid comprising at least 12carbon atoms and of glycerol.

The mono fatty acid may be saturated or unsaturated and in particularmay be stearic acid, lauric acid, myristic acid, palmitic acid, erucicacid, oleic acid or linoleic acid. Preferably, the compound (D) isglyceryl monostearate.

Preferably, the amount by weight of compound (D) ranges from 0.3 to 1.65parts, advantageously from 0.5 to 1.5 parts, preferentially from 0.65 to1.3 parts, these amounts by weight being expressed relative to 100 partsof the dry weight of the various constituents (A), (B) and (C).

In these particular variants, the compound (D) makes it possible toobtain films, by extrusion blow molding, with particularly lowtackiness.

Preferably, the amount by weight of compound (D) is less than 8 parts,preferably less than 5 parts, most preferentially less than 2.5 parts,these amounts by weight being expressed relative to 100 parts of the dryweight of the various constituents (B) and (C).

The composition according to the invention may also comprise otheradditives or additional polymers, termed additional constituents, or amixture thereof.

The composition according to the invention can in particular alsocomprise a bonding agent bearing several functions capable of reactingwith the polyester and/or the starch and/or the organic plasticizer forstarch, it being possible for this function to be chosen from carboxylicacid, carboxylic acid ester, isocyanate or epoxy functions. This bondingagent, in particular citric acid, can be present in an amount by weightranging from 0.01 to 0.45 part, these amounts by weight being expressedrelative to 100 parts of the total dry weight of (A), (B) and (C).Advantageously, the composition comprises from 0.05 to 0.3 part ofcitric acid, preferentially from 0.06 to 0.20 part, most preferentiallyfrom 0.07 to 0.15 part, these amounts by weight being expressed relativeto 100 parts of the total dry weight of (A), (B) and (C). The presenceof citric acid in the composition makes it possible to improve thehomogeneity thereof and thus to improve the properties of thecomposition. In the citric acid proportions selected and particularly inthe preferred proportions, the composition is easy to granulate, incomparison with the compositions based on polyester and thermoplasticstarch comprising larger amounts of citric acid.

The composition according to the present invention can also comprise, asother additive or additional constituent, fillers or fibers of organicor inorganic nature, which are optionally nanometric and optionallyfunctionalized. They may be silicas, zeolites, glass fibers or beads,clays, mica, titanates, silicates, graphite, calcium carbonate, talc,carbon nanotubes, wood fibers, carbon fibers, polymer fibers, proteins,cellulose-based fibers, lignocellulosic fibers and non-destructuredgranular starch. These fillers or fibers can make it possible to improvethe hardness, the rigidity or the water- or gas-permeability.Preferably, the composition comprises from 0.1 to 200 parts of fillersand/or fibers, for example from 0.5 to 50 parts, this amount beingexpressed relative to 100 parts of the total dry weight of (A), (B) and(C). The composition may also be of composite type, i.e. may compriselarge amounts of these fillers and/or fibers.

The additive that is of use in the composition according to theinvention may also be chosen from opacifiers, dyes and pigments. Theymay be chosen from cobalt acetate and the following compounds: HS-325Sandoplast® Red BB (which is a compound bearing an azo function, alsoknown under the name Solvent Red 195), HS-510 Sandoplast® Blue 2B whichis an anthraquinone, Polysynthren® Blue R, and Clariant® RSB Violet.

The composition according to the invention may also comprise otheradditives, such as stabilizers, for example light stabilizers, UVstabilizers and heat stabilizers, fluidizers, flame retardants andantistatic agents. It may also comprise primary and/or secondaryantioxidants. The primary antioxidant may be a sterically hinderedphenol, such as the compounds Hostanox® 0 3, Hostanox® 0 10, Hostanox® 016, Ultranox® 210, Ultranox®276, Dovernox® 10, Dovernox® 76, Dovernox®3114, Irganox® 1010 or Irganox® 1076. The secondary antioxidant may betrivalent phosphorus compounds such as Ultranox® 626, Doverphos® S-9228,Hostanox® P-EPQ or Irgafos® 168.

The composition may also comprise, as additive, an additional processingaid, different than the compound (D), making it possible to reduce thepressure in the processing tool. These aids can also have the functionof demolding agents making it possible to reduce the adhesion to thematerials for forming the composition, such as molds or calenderingcylinders. These aids may be selected from fatty acid esters and fattyacid amides different than the compound (D), metal salts, soaps,paraffins and hydrocarbon-based waxes. Particular examples of these aidsare zinc stearate, calcium stearate, aluminum stearate, stearamides suchas ethylene bis(stearamide) (EBS), erucamide such as Incromax®,behenamide, beeswaxes or candelilla wax. According to this preferredvariant, this additional processing aid may be present in an amount byweight of less than 0.2 part, advantageously in an amount by weight ofless than 0.1 part, these amounts by weight being expressed relative to100 parts of the total dry weight of the constituents (A), (B) and (C).However, the composition according to the invention is preferably freeof additional processing aid. Processing aids such as erucamides can bedifficult to meter out and can lead to problems during the use of thefilms (difficulty with printing, bubble instability during the extrusionblow molding step).

The composition may also comprise an additional polymer, different thanthe polyester(s) (A). This polymer may be chosen from polyamides,polystyrene, styrene copolymers, styrene-acrylonitrile copolymers,styrene-acrylonitrile-butadiene copolymers, poly(methyl methacrylate)s,acrylic copolymers, poly(ether-imide)s, poly(phenylene oxide)s, such aspoly(2,6-dimethylphenylene oxide), poly(phenylene sulfate)s,poly(ester-carbonate)s, polycarbonates, polysulfones, polysulfoneethers, polyether ketones, and mixtures of these polymers.

The composition may also comprise, as additional polymer, a polymer forimproving the impact properties of the polymer, in particular functionalpolyolefins such as functionalized ethylene or propylene polymers andcopolymers, core-shell copolymers or block copolymers.

The compositions according to the invention may also comprise polymersof natural origin, such as cellulose, chitosans, alginates,carrageenans, agar-agar, proteins such as gluten, pea proteins, casein,collagen, gelatin or lignin, these polymers of natural origin possiblybeing physically or chemically modified.

According to one variant of the invention, the composition comprises bydry weight:

-   -   from 10 to 80 parts of at least one polyester (A1) from        condensation of ethylene glycol and of 1,4-butanediol and of        succinic acid and/or of adipic acid, preferably from 30 to 55        parts, most preferentially from 30 to 50 parts;    -   from 5 to 50 parts of at least one starch (B), preferably from        20 to 40 parts;    -   from 5 to 50 parts of at least one organic plasticizer (C) for        starch, preferably from 10 to 35 parts;    -   optionally from 1 to 70 parts of polylactic acid (A2),        preferably from 5 to 35 parts; the sum of the amounts of        constituents (A1), (A2), (B) and (C) coming to 100 parts; the        composition also comprising:    -   from 0.05 to 1.7 parts of monoester (D) of a mono fatty acid        comprising at least 12 carbon atoms and of glycerol,        advantageously from 0.3 to 1.65 parts, preferentially from 0.5        to 1.5 parts, most preferentially from 0.65 to 1.3 parts;    -   optionally from 0.01 to 200 parts of additional constituent(s)        chosen from the additives and polymers, different than (A1),        (A2), (B), (C) and (D).

The composition according to the invention can be manufactured using amanufacturing process comprising:

-   -   a step a) of introducing into a mixing system constituents        comprising at least one aliphatic polyester (A), at least one        starch (B), at least one organic plasticizer for starch (C), at        least one monoester (D) of a mono fatty acid comprising at least        12 carbon atoms and of glycerol, and optionally water;    -   a mixing step b) in which the constituents are        thermomechanically mixed so as to obtain the thermoplastic        composition;    -   a step c) of recovering the thermoplastic composition.

The amounts of the various constituents can obviously be varied in sucha way as to obtain the compositions described above. In the case whereconstituents comprising moisture are used, those skilled in the art caneasily, in order to carry out the process, determine the amounts byweight of the various constituents by wet weight to be introduced intothe mixing system, by measuring beforehand the moisture content in eachconstituent, for example by carrying out an assay using the Karl-Fishermethod, this being in order to obtain the compositions in theproportions described above. By way of illustration, the Examplessection contains the description of compositions expressed by dryweight, with the amounts of each of the constituents used during theprocess which are, for their part, expressed by wet weight.

With regard to the mixing system, it may involve internal blade or rotormixers, external mixers, or single-screw or co-rotating orcounter-rotating twin-screw extruders. However, it is preferred toprepare this mixture by extrusion, in particular using a co-rotatingtwin-screw extruder. In the case of an extruder, the variousconstituents of the composition may be introduced by means of feedhoppers located along the extruder.

The process described in WO 2010/010282 A1 may in particular be used toprepare the composition.

The mixing system may comprise a drying system, for example a system forextracting the volatile compounds, such as a vacuum pump. In this case,the moisture content of the composition at the end of the process may bereduced in comparison with the total moisture content of theconstituents introduced in step a).

Preferably, the moisture content of the composition is adjusted so as tobe between 2.5% and 9% relative to the total weight (and thus wetweight) of the constituents introduced during step a).

Advantageously, the process comprises at least one drying step, suchthat the moisture content of the composition is between 0.2% and 1.4%.Preferably, the mixing of step b) is carried out simultaneously with thedrying step, for example by connecting a vacuum pump to the reactor. Theprocess may also comprise a distinct drying step, which takes placesubsequent to the recovering step c).

According to the invention, the mixing temperature during step b)advantageously ranges from 90 to 210° C., preferentially from 110 to190° C.

The mixing of the constituents of the composition may take place underan inert atmosphere.

With regard to the mixing system, it may involve internal blade or rotormixers, external mixers, or single-screw or co-rotating orcounter-rotating twin-screw extruders. Preferably, the mixing step b)takes place in an extruder, in particular using a co-rotating twin-screwextruder. When it is by extrusion, the step a) of introducing thevarious constituents of the composition can be carried out by means ofintroduction hoppers located along the extruder.

When the mixing is carried out by extrusion, the composition recoveredin step c) is in the form of a rod of polymer.

Preferably, the manufacturing process also comprises a step d) ofgranulating the composition recovered in step c). At the end of thisgranulating step d), granules of composition are obtained.

This granulating step can be carried out by means of any type ofgranulator, for example a water ring granulator, an underwatergranulator or a rod granulator. The composition recovered can be veryeasily granulated, this being without bead formation, in particular whenthe composition comprises citric acid.

The invention also relates to granules of polymer consisting of thecomposition according to the invention.

The invention also relates to an article comprising the compositionaccording to the invention.

This article may be of any type and may be obtained using conventionaltransformation techniques.

It may be, for example, fibers or threads that are of use in the textileindustry or other industries. These fibers or threads may be woven so asto form fabrics, or else nonwovens.

The article according to the invention may also be a film or a sheet.These films or sheets may be produced by calendering, film castextrusion or blown film extrusion techniques.

The invention relates in particular to a process for manufacturing afilm by film blowing, comprising:

-   -   a step of extruding the composition or granules according to the        invention so as to form a molten composition;    -   a step of forming a blown tube by blowing the molten composition        obtained in the following step;    -   a step of drawing the blown tube;    -   a step of recovering a film.

Advantageously, the drawing speed is greater than 5 m/s, preferablygreater than 10 m/s. The compositions according to the invention, inparticular in the preferred variants, make it possible to keep excellentproduction rates and to obtain high drawing speeds, in particular whenthe composition comprises a blend of polyesters (A1) and (A2).

The article according to the invention may also be a container fortransporting gases, liquids and/or solids. The containers concerned maybe bottles, for example sparkling or still water bottles, juice bottles,soda bottles, carboys, alcoholic drink bottles, small bottles, forexample small medicine bottles, small bottles for cosmetic products,dishes, for example for ready meals, microwave dishes, or lids. Thesecontainers may be of any size. They may be produced by extrusion-blowmolding, thermoforming or injection-blow molding.

The articles may also be multilayer articles, at least one layer ofwhich comprises the composition according to the invention. Thesearticles may be produced via a process comprising a coextrusion step inthe case where the materials of the various layers are placed in contactin the molten state. By way of example, mention may be made of thetechniques of tube coextrusion, profile coextrusion, coextrusionblow-molding of a bottle, a small bottle or a tank, generally collatedunder the term “coextrusion blow-molding of hollow bodies”, coextrusionblow-molding also known as film blowing, and cast coextrusion.

They may also be manufactured according to a process comprising a stepof applying a layer of molten composition onto a layer based on organicpolymer, paper, metal or adhesive composition in the solid state. Thisstep may be performed by pressing, by overmolding, stratification orlamination, extrusion-lamination, coating, extrusion-coating orspreading.

The invention will now be illustrated in the examples hereinafter. It ispointed out that these examples do not in any way limit the presentinvention.

EXAMPLES Constituents

The constituents of the various compositions illustrated are presentedbelow.

(A): Polyesters

(A1): Aliphatic polyester from condensation of succinic acid, of adipicacid and of 1,4-butanediol, melting point of 95° C., flow index equal to1.2 g/10 min.

(A2): Semi-crystalline poly(lactic acid) (L-lactic acid content equal to9.75 mol %, D-lactic acid content equal to 4.3 mol %, melting point of150° C., flow index equal to 2.6 g/10 min).

(B): Starch

Starch a: Wheat starch (containing 12.5% water)

Starch b: Potato flour (containing 20% water)

(C): Plasticizer

Plasticizer c: Glycerol

Plasticizer d: Mixture of glycerol and sorbitol containing 16% of waterwith the distribution by dry weight glycerol=60%, sorbitol=40%.

(D) Monoester Compound

(D)=Glyceryl monostearate

Additives

Processing aids other than compound (D)

Incromax®

EBS: ethylene bis(stearamide)

Bonding agent

CA=Citric acid

Composition Manufacturing Process

The compositions according to the invention and comparative compositionswere prepared using an extruder of the Leistritz brand, ZSE27MAXX60D,Diameter 28, Length L/D=60, for a flow rate of: 20 kg/h.

-   -   Temperature profile (fifteen heating zones Z1 to Z15,        temperature in ° C.):        20/60/60/80/90/110/130/130/180/160/180/150/130/130/130 with a        variable screw speed of 200 rpm to 400 rpm.

In the case where the composition envisioned comprises an additionalpolyester, physical mixing of the granules of the polyesters (A1) and(A2) is carried out prior to the introduction into the extruder.

During the process, the following are introduced into the extruder:

-   -   the polyester (A) or the blend of the polyesters (A1) and (A2)        in the main hopper of the extruder, following which said blend        passes through all of the heating zones of the extruder,    -   the plasticizer for starch (C) in zone Z3 (9 to 12 D),    -   the starch (B), and also the additives at zone Z4 (13 to 16 D).

A partial vacuum is applied in zone Z9 (33-36 D) and in zone 11 (41-44D) (vacuum of 100 mbar) making it possible to remove the water.

The granules are obtained by means of a conventional underwatergranulation system.

The granules are dried in a basket dryer for 2 hours at 80° C. Moisturecontent is assayed using the Karl-Fisher method. All the compositionsobtained have a moisture content of approximately 0.5%.

Details of the Compositions

The compositions according to the invention and the comparativecompositions were prepared using the process described above. Theamounts of the various constituents introduced into the extruder aregiven in table 1. The proportions of all the constituents are givenrelative to the wet weight of the sum of the constituents (A), (B) and(C).

In order to facilitate reading, it is specified that a compositionaccording to the invention is named EX and a comparative composition isnamed Comp EX.

TABLE 1 Proportion of the constituents of the compositions by wet weightintroduced into the extruder (A1) (A2) (B) (C) (D) EBS Incromax CA Ex 132.12 13.77 35.17^(a) 18.94^(c) 0.66 0 0 0.1 Ex 2 32.12 13.77 35.17^(a)18.94^(c) 0.95 0 0 0.1 Ex 3 32.12 13.77 35.17^(a) 18.94^(c) 1.18 0 0 0.1Ex 4 32.12 13.77 35.17^(a) 18.94^(c) 1.41 0 0 0.1 Ex 5 26.6 17.7436.18^(a) 19.48^(d) 0.92 0 0 0.09 Ex 6 26.6 17.74 36.18^(a) 19.48^(d)1.14 0 0 0.09 Ex 7 26.6 17.74 36.18^(a) 19.48^(d) 1.37 0 0 0.09 Ex 834.77 23.18 27.33^(a) 14.71^(c) 0.67 0 0 0.1 Ex 9 31.74 21.6 30.62^(a)16.49^(c) 0.67 0 0 0.1 Ex 10 27.53 18.35 35.13^(a) 18.93^(c) 0.67 0 00.1 Ex 11 27.53 18.35 35.13^(a) 18.93^(c) 0.29 0 0 0.1 Ex 12. 34.94 8.734.94^(b) 11.26^(c) 0.95 0 0 0.1 Ex 13 32.12 13.77 35.17^(a) 18.94^(c)0.95 0 0 0.18 Comp 32.12 13.77 35.17^(a) 18.94^(c) 0 0 0 0.1 Ex 1 Comp32.12 13.77 35.17^(a) 18.94^(c) 0 0.29 0 0.1 Ex 2 Comp 32.12 13.7735.17^(a) 18.94^(c) 0 0.48 0 0.1 Ex 3 Comp 32.12 13.77 35.17 to18.94^(c) 0 0.95 0 0.1 Ex 4 12 Comp 32.12 13.77 35.17^(a) 18.94^(c) 1.880 0 0.1 Ex 5 Comp 32.12 13.77 35.17^(a) 18.94^(c) 0 0 0.29 0.1 Ex 6 Comp32.12 13.77 35.17^(a) 18.94^(c) 0 0 0.95 0.1 Ex 7

Table 2 expresses the proportions by weight of the various constituentsof the composition recovered in the form of dry granules, these amountsbeing expressed relative to 100 parts of the total dry weight of theconstituents (A), (B) and (C).

TABLE 2 Proportion of the constituents by dry weight in the compositionsextruded (A1) (A2) (B) (C) (D) EBS Incromax CA Ex 1 33.6 14.4 32.19^(a)19.81^(c) 0.7 0 0 0.1 Ex 2 33.6 14.4 32.19^(a) 19.81^(c) 1 0 0 0.1 Ex 333.6 14.4 32.19^(a) 19.81^(c) 1.25 0 0 0.1 Ex 4 33.6 14.4 32.19^(a)19.81^(c) 1.5 0 0 0.1 Ex 5 28.8 19.2 34.28^(a) 17.72^(d) 1 0 0 0.1 Ex 628.8 19.2 34.28^(a) 17.72^(d) 1.25 0 0 0.1 Ex 7 28.8 19.2 34.28^(a)17.72^(d) 1.5 0 0 0.1 Ex 8 36 24 24.76^(a) 15.24^(c) 0.7 0 0 0.1 Ex 9 3322 27.86^(a) 17.14^(c) 0.7 0 0 0.1 Ex 10 28.8 19.2 32.19^(a) 19.81^(c)0.7 0 0 0.1 Ex 11 28.8 19.2 32.19^(a) 19.81^(c) 0.3 0 0 0.1 Ex 12. 38.49.6 39.6^(b) 12.38^(c) 1 0 0 0.1 Ex 13 33.6 14.4 32.19^(a) 19.81^(c) 1 00 0.2 Comp Ex 1 33.6 14.4 32.19^(a) 19.81^(c) 0 0 0 0.1 Comp Ex 2 33.614.4 32.19^(a) 19.81^(c) 0 0.3 0 0.1 Comp Ex 3 33.6 14.4 32.19^(a)19.81^(c) 0 0.5 0 0.1 Comp Ex 4 33.6 14.4 32.19^(a) 19.81^(c) 0 1 0 0.1Comp Ex 5 33.6 14.4 32.19^(a) 19.81^(c) 2 0 0 0.1 Comp Ex 6 33.6 14.432.19^(a) 19.81^(c) 0 0 0.3 0.1 Comp Ex 7 33.6 14.4 32.19^(a) 19.81^(c)0 0 1 0.1

In addition, comparative compositions 8, 9, 10 and 11 were prepared.These compositions differ from the compositions of the examplesaccording to the invention 2, 5, 12 and 13 in that glucose stearate isused instead of glyceryl monostearate.

The granules of the compositions obtained above were converted into theform of a blown tube according to the following protocol: the granulesof the compositions are converted into films on a blow-molding extruderof the Collin brand (Diameter 20, Length L/D=18, five heating zones Z1to Z5) using the following temperature profile (160° C./160° C./160° C./160° C. /160° C.) and a screw speed of 60 revolutions per minute. Themaximum blown tube manufacturing speed, and also the ratio of this speedrelative to the maximum speed of the machine are reported in table 3.

The tacky aspect of the blown tubes was evaluated in two ways:

-   -   the tendency of the blown tube to stick to itself after having        been rolled up;    -   the tacky feel of the blown tube.

The mechanical properties were also measured when the blown tube couldbe separated so as to form a 50 μm film. The evaluation of the tackyaspect and also the mechanical properties are also reported in table 3.

TABLE 3 Evaluation of the film-forming ability and of the films obtainedby blown film extrusion Tacky Stickiness Drawing Ds/Ds Moduluselongation feel to itself speed (m/s) max. % (MPa) at break (%) ++ ++ 13100 250 250 Ex 2 ++ ++ 13 100 280 225 Ex 3 ++ ++ 13 100 220 225 Ex 4 ++++ 7.8 60 195 190 Ex 5 ++ ++ 13 100 260 220 Ex 6 ++ ++ 13 100 215 190 Ex7 ++ ++ 7.15 55 255 195 Ex 8 ++ ++ 13 100 275 230 Ex 9 ++ ++ 13 100 240195 Ex 10 ++ ++ 13 100 170 165 Ex 11 + + 13 100 295 270 Ex 12. ++ ++ 13100 140 245 Ex 13 ++ + 13 100 340 115 Comp Ex 1 −− −− 9.1 70 NA NA CompEx 2 − −− 13 100 NA NA Comp Ex 3 − −− 13 100 NA NA Comp Ex 4 − −− 13 100NA NA Comp Ex 5 NA NA NA Film NA NA formation not possible Comp Ex 6 −−− 13 100 NA NA Comp Ex 7 − −− 13 100 NA NA Tackiness grading Feel:++does not stick, non-greasy +slightly greasy feel −greasy and waxy−−tacky Blown tube: ++Blown tube separated +Blown tube can be easilyseparated −Blown tube can be separated by tensile force −−Blown tubestuck and cannot be separated

The tests show that the use of a monoester of a mono fatty acid and ofglycerol in compositions based on thermoplastic starch and aliphaticpolymer makes it possible, when the amount is less than 2 parts, thisamount being expressed relative to 100 parts of the total dry weight ofthe constituents (A), (B) and (C), to form non-tacky films by filmblowing.

The films can be formed at high speed, in particular when the amount ofmonoester of a mono fatty acid and of glycerol ranges from 0.3 to 1.25parts. However, if films which do not stick at all are desired, it isadvantageous to use amounts of 0.5 part or more. Conversely, when otherprocessing aids, such as Incromax® or EBS, are used, this beingregardless of the amount used, all the blown tubes formed are very tackyand it is thus not possible to open the blown tube. The sameobservations were made for comparative compositions 8 to 11. Thus,compared with the compositions of application WO2007/012142, whichcomprise glucose stearate, the compositions according to the inventioncan be converted at higher rate by blowing in the form of a blown tube,without said blown tube sticking to itself.

It may be noted that it was impossible to form a film (it was notpossible to form the blown tube), when the amount of monoester of a monofatty acid and of glycerol is 2 parts.

1. A thermoplastic composition comprising at least one polyester (A)which is an aliphatic polyester, at least one starch (B), at least oneorganic plasticizer for starch (C), and at least one compound which is amonoester (D) of a mono fatty acid comprising at least 12 carbon atomsand glycerol wherein 0.05 to 1.7 parts of compound (D) by weight,relative to 100 parts of the dry weight of the various constituents (A),(B) and (C), are present.
 2. The composition according to claim 1,wherein 0.3 to 1.65 parts of compound (D) are present.
 3. Thecomposition according to claim 1, wherein compound (D) is glycerylmonostearate.
 4. The composition according to claim 1, wherein that thepolyester said aliphatic polyester comprises polylactic acid (A2),polymers (A1) produced from condensation of ethylene glycol and/or of1,4-butanediol and of succinic acid and/or of adipic acid, and mixturesthereof.
 5. The composition according to claim 4, wherein said at leastone polyester comprises a blend of polymers (A1) and (A2), a weightpercentage of (A2) relative to a weight of (A1) and (A2), expressed bydry weight, ranges from 5% to 90%.
 6. The composition according to claim1, wherein said polyester (A) comprises from 35 to 75 parts relative to100 parts of the total dry weight of the constituents (A), (B) and (C).7. The composition according to claim 1, wherein a starch/plasticizerweight ratio, expressed by dry weight, ranges from 90/10 to 40/60. 8.The composition according to claim 1, wherein the organic plasticizercomprises diols and polyols, including glycerol, polyglycerols,sorbitans, sorbitol, mannitol, and hydrogenated glucose syrups, urea,polyethers with a molar mass below 800 g/mol, and mixtures thereof. 9.The composition according to claim 1 comprising a morphology includingco-continuous domains of thermoplastic starch and polyester.
 10. Thecomposition according to claim 1, wherein polyester (A) has a flow indexranging from 0.1 to 50 g/10 min in accordance with ISO 1133, at 190° C.and 2.16 kg.
 11. A granule of polymer comprising the composition ofclaim
 1. 12. A process for manufacturing a thermoplastic composition,comprising: introducing into a mixing system constituents comprising atleast one aliphatic polyester (A), at least one starch (B), at least oneorganic plasticizer for starch (C), at least one monoester (D) of a monofatty acid comprising at least 12 carbon atoms and of glycerol, andoptionally water; thermomechanically mixing the constituents to obtain athermoplastic composition; and recovering the thermoplastic composition.13. The process according to claim 12, further comprising introducingwater and adjusting moisture content of the constituents to between 2.5%and 9%; and wherein said thermomechanical mixing is carried outsimultaneously with drying to adjust the moisture content of therecovered composition between 0.2% and 1.4%.
 14. The process accordingto claim 12, wherein a twin-screw extruder performs the thermomechanicalmixing.
 15. A process for manufacturing a film by film blowing,comprising: extruding one of a composition comprising at least onealiphatic polyester (A), at least one starch (B), at least one organicplasticizer for starch (C), at least one monoester (D) of a mono fattyacid comprising at least 12 carbon atoms and of glycerol, and optionallywater, or a granulated thermoplastic composition comprising at least onealiphatic polyester (A), at least one starch (B), at least one organicplasticizer for starch (C), at least one monoester (D) of a mono fattyacid comprising at least 12 carbon atoms and of glycerol, and optionallywater to form a molten composition; forming a blown tube by blowing saidmolten composition; drawing the blown tube; and recovering a film